If a man has all the signs of being toxic can he change with another partner?

We can sit and analyze and analyze and analyze but I think the most important point here that you made was that you realized that he was in fact the one with the problem, something to remember is that nobody can make us feel anything, in order to do that we need to allow them to make us feel a certain way i.e low self esteem, not worthy etc. If he does get married or not, or if their relationship works out etc is really immaterial, you have moved on and that is all that matters, well done.